A pizza cook who admitted making a hoax call warning of liquid explosives on a plane, causing the flight to be diverted, must write an apology letter to every delayed passenger.

Kenneth Smith Jr., 26, pleaded guilty Monday to malicious false information about an explosive, and false information and hoaxes, according to a press release from the U.S. Attorney’s Eastern District of Pennsylvania Office.

Smith faces up to 15 years in prison and fines of up to $500,000 when he is sentenced on April 16. He has agreed to pay restitution and write an apology letter to every passenger who was on the flight when it was delayed, and reimburse the emergency response costs, prosecutors said.

Smith’s reasoning for the hoax, according to federal prosecutors, was to target a passenger on the flight, Christopher Shell, who was at the time identified as the ex-boyfriend of Smith’s girlfriend.

Reportedly Shell had posted a compromising photo of the woman on Facebook.